1. Field of the Invention
The present invention relates to machining and, more particularly, to drilling holes, slots and other passageways through a workpiece by electron beam and other beam energy techniques.
2. Description of the Prior Art
The use of electron beam energy to drill one or more holes in a metallic or nonmetallic workpiece has only recently been investigated. As described in copending patent application Ser. No. 861,776, filed Dec. 19, 1977, entitled "Backer Layer For Electron Beam Drilling" of inventors Lester W. Jordan, Curtiss G. Howard and Chester E. Yaworsky and of common assignee herewith, a so-called backer layer generally in the form of a coating is required on the last penetrated surface of the workpiece during the drilling process. The purpose of the backer layer is to absorb excess electron beam energy as the beam penetrates the last penetrated workpiece surface and to generate sufficient vapor pressure by action of the beam locally thereon to expel the molten workpiece material from the hole being drilled in a direction opposite to the propagation of the electron beam, that is, from the entrance to hole in the first penetrated surface of the workpiece. However, as a result of this expulsion of molten material from the hole, there has been experienced a problem of burr formation around the perimeter of the hole in the first penetrated surface. Burrs appear to form from the molten spatter that is expelled from the hole and subsequently welds to the first penetrated surface in the vicinity of the hole perimeter. An expensive metal finishing operation is required to remove the burrs from the hole perimeter.
In the development of electron beam drilling, the parameters of drilling, such as beam energy, pulse duration and focus level, have been adjusted in attempts to minimize formation of burrs around the hole perimeter. However, to date, such attempts have not proved effective, especially from a commercial production standpoint.